There's an unwritten rule when it comes to playing iconic characters: stick to one at a time. Sean Connery understood it (at least in his classic years as 007), Christopher Reeve got it, and so, it seems, does Daniel Craig. According to Iesb.com, the blond Bond was offered the role of Thor in Marvel's forthcoming adaptation of the adventures of the Norse god, and turned it down, reportedly stating that the dual roles would have been "too much of a power trip".

The thought of having one actor playing both 007 and the son of Odin isn't the only reason why I think Craig made the right choice here. Thor looks set to be directed by Kenneth Branagh, whose involvement immediately implies something more highbrow, but I'm struggling to see how the finished product can possibly end up being anything other than high camp. It seems to me that the respected directors who are currently signing on in their droves to bring comic book characters to the big screen have most likely been influenced by Christopher Nolan's successful attempt to excise every last gram of cheese from the Batman franchise. The problem is that Batman is an inherently more complex character, with enormous potential for pseudo-psychological analysis. I even have a book sitting, admittedly unread, next to my bed titled Batman and Philosophy, which attempts to explain many of the essential tenets of western and eastern thinking through the filter of Bruce Wayne's alter ego.

Thor, on the other hand, is a bloody great viking who looks like a participant in a professional wrestling contest. Craig, who has worked so hard to rebuild audiences' belief in 007 as an inhabitant of the real world, would have been a laughing stock. The only similar successful figure in celluloid is Robert E Howard's Conan, the subject of John Milius's bravura 1982 epic fantasy starring a perfectly cast Arnold Schwarzenegger, and one abominably cheesy sequel. But the difference is that Conan didn't have to visit the modern day real world. Thor is going to suffer hugely from what I like to call the Hercules in New York syndrome: dress him in jeans and he looks stupid, keep him in his original garb and, well, he still looks pretty damn stupid.

Besides, I met Craig recently and despite the buffness he's not a particularly big man in real life; I'd say he's at least six inches too short to play a Norse god. Who do you think would make a good Thor?

The not-more-than-one icon rule (catchy, eh?) is the reason why I'm more than a little concerned about Christian Bale's decision to take on the role of John Connor in (shudder) McG's Terminator: Salvation. For me, when an actor takes on parts which aren't worthy of them, or just plain wrong, it ruins my enjoyment of their performances in other films, and I really want to see more of Christian Bale as Batman.

A good example of an actor breaking this rule is Samuel L Jackson. Thanks to roles in Snakes on a Plane and the Star Wars prequels, he has become a ridiculous caricature of himself. That obscenely charismatic turn as Jules Winnfield in Pulp Fiction has almost haunted him; people now expect larger-than-life acting from his films, and with a few exceptions, that's exactly what they get.

Still, Jackson could be good value as Nick Fury, a role he confirmed earlier this week, in the forthcoming Iron Man 2. Those who've seen Jon Favreau's summer superhero blockbuster may remember the post credits scene in which Jackson appears as the head of S.H.I.E.L.D, a mysterious organisation aimed at fighting the world's nefarious forces. Marvel comics has already remoulded Fury to fit Jackson's appearance and personality, and the actor will no doubt get off on playing a character who is effectively immortal and has been at one time or another, a second world war colonel, a suave 60s super-spy and modern day defeater of alien invaders. The fan-boys seem to have forgiven the actor for the whole purple lightsabre debacle: hopefully the Iron Man sequel will give him enough of a part that he can remind us why he was such a fascinating screen presence in the first place.

"The truth is that Hulk has had two films in the past five years, and it's time to give some of the other guys a turn," Feige told MTV News. "But certainly what we are doing is suggesting and cross-pollinating the characters between films, and, like reading a comic, I'd like to set that expectation that anything can happen - and anyone can pop up - in anybody else's story. I would expect that people may see the Hulk again soon before he is again carrying his own film."

This implies that the Hulk could, as predicted in this column, end up in the forthcoming Avengers movie, which will likely unite Iron Man, Captain America and Thor. Where that leaves Ed Norton is anybody's guess. Feige also said that Marvel were considering bringing Doctor Strange to the big screen, a quite intriguing prospect. The character isn't among the comic book publisher's best known, but that could work in its favour. Strange is a sorceror who, in his most recent incarnation, serves chiefly as a supporting character that superheroes often turn to for matters concerning the supernatural.

The fact that Strange's name is coming up at all suggests that Marvel, which, lest we forget, has only produced two films so far, is thinking beyond its current roster of Iron Man 2, Thor, The Avengers and Ant Man, which alone should take the studio up until at least 2011. That's all very well, but I hope the quality control remains high: just as actors can take on too many roles, studios can take on too many projects. These films need to be great movies, not just great comic book movies, if they are to appeal beyond fan-boy circles, as the Dark Knight and Iron Man did this summer. Perhaps Marvel should follow Craig's lead, and take things one at a time too.